Jimmy,
The "beast" can be tamed and in most locations the F-70 can be dialed up way beyond the factory defaults. I now have two F-70's, one has the standard 10" coil and the other has the 11" DD coil. I also have the 6.5 inch elliptical coil that I use in trashy locations. My experience is that once in a while you will find a location where the F-70 is unusable. My backyard is a perfect example. When I am in my back yard within 25 feet of my house both F-70's go crazy due to some sort of EMI; however, when I walk approximately 50' feet away both detectors return to being rock solid stable. So far, this is the only location where I have encountered any problems.
I can usually run my F-70 at sensitivity at 85, Threshold at 0, DE mode, Tones at 2F, Disc at 5 with no hint of instability in most locations. I prefer to set the discrimination low so I can hear and evaluate each target not only by VDI but by sound and depth. I have found that the 11" DD coil is not only a little deeper but also makes the detector more stable and is a pinpointing dream; almost every target that I dig using the 11" coil is dead center in the plug with the only exception being a coin that is standing on its edge. Furthermore, the 11 coil does not seem to up-average deep targets like the stock coil does. I have a quarter buried at 12" in the back yard and the F-70 with the stock coil gives a VDI of 90+ but when I change to the 11" DD coil the VDI gives a correct reading of 82.
If you want some SERIOUS depth and the area you are searching is free of a lot of junk targets run the F-70 in At motion all-metal mode, Speed SL Threshold -5 (or lower) and you will be totally blown away how deep this machine truly is. In auto-tune mode you may need to play around with the sensitivity and threshold a little to find a setting you can work with; however, even at the lower settings there are very few targets that are going to escape detection. Even when running in motion all-metal mode the F-70 still provides you with VDI target ID.
Comments Welcome,
Leo